1. Field of the Invention
The present invention relates to the detection of gases produced by incipient faults in electrical equipment, and more particularly in electrical transformers.
2. Description of the Prior Art
It has long been recognized by the electrical industry that abnormal electrical and thermal stresses in electrical apparatus are invariably accompanied by degradation of the surrounding insulating material. In oil/paper insulating systems, this degradation is accompanied by the production of a number of gases. These are principally hydrogen, carbon monoxide and carbon dioxide and low molecular weight hydrocarbons. The rate of generation of these gases and their composition is a function of fault severity, i.e., rate of energy dissipation and temperature, and of fault type (hot spot, arcing, partial discharges, etc.).
At the high generation rates characteristic of an actual fault, this phenomenon has been utilized for many years to activate gas sensitive alarms and protective relays. However, it has also been recognized that reliable detection of fault gases, before the generation rate becomes large enough to activate such device, can provide invaluable early warning of incipient fault development.
Detectors have been developed which continuously monitor gases resulting from incipient faults, such as in U.S. Pat. No. 3,680,359, Lynch, 1972. However, the monitor described in this patent appears limited to gas cushioned transformers and is based on detection of hydrogen by measurement of the thermal conductivity of the gas which comprises the gas cushion. Such detection is made possible by the fact that hydrogen has a much higher thermal conductivity than the nitrogen which is the main component in the gas cushion. The monitor includes means to continuously test the thermal conductivity, and as the thermal conductivity of the gas blanket increases above the base conductivity, a warning will be emitted by the monitor. The Lynch type of monitor does not appear useful in a completely oil filled apparatus such as conservator and diaphragm sealed power transformers or in sealed instrument transformers.
In U.S. Pat. No. 3,559,457, Collins, 1971, there is described a hydrogen detector for use in a transformer tank which includes a tube formed of palladium alloy which will expand in the presence of hydrogen. Indicator means are connected to the tube to display the amount of its axial expansion. This device has probably relatively low detectability and is probably relatively insensitive. It would also appear that the hydrogen detector of this patent must be used in a gaseous environment, such as in the nitrogen cushion over the oil insulator in a transformer. It is not believed that the device shown in this patent could be utilized in an oil sealed transformer to detect dissolved hydrogen.